The Water Bag Project

Revegetation Project at Calperum Station in 2018/2019.
This project was planned by Dr. Peter Cale, Calperum Station Manager, and managed by David Gooley of the Rotary Club of Mitcham.
The aim of the project is to evaluate the watering of seedlings by a refillable 25 litre vinyl water bag rather than the current system of 1000 litre tanks feeding water to the seedlings via 19mm irrigation hoses and drippers.
The current watering frequency varies from weekly in the summer to irregularly in the remainder of the year depending on weather conditions. For the Water Bag trial, each seedling is surrounded by a vinyl 25 litre bag laid on the ground. The water drips slowly from the bag to the ground adjacent to the seedling providing continuous moisture for the seedling for up to a month. The bag requires refilling every 4 weeks. The bag acts as mulch for the ground, minimising the moisture evaporation and minimising weed growth.
A special thanks to Norm Hood, Rotary Club of Renmark for his generous donation for the purchase of 50% of the bags.
Advantages of the Water Bag.
  1. For the first 12 months, the seedling will have near continuous moisture aiding plant growth, depending on the drip rate and the atmospheric conditions. After the 12 months the bags will not be refilled every month to permit the soil to dry out causing the plant to generate root growth further into the ground improving dry conditions/drought resistance.
  2. The number of man hours required for watering per surviving plant may be less. We will not know this until the end of the trial. The bag refilling during the trial will be done by volunteer Rotarians.
 
Disadvantages of the Water Bags.
  1. The bag is made of medium grade vinyl. It has a narrow outlet through which a cloth wick passes. The water drips from the wick, with an ideal distance out of the outlet being 25mm. The presence of the moist wick will attract the native and non-native animals, searching for water. They may damage the wick and adversely affect the dripping. The bags are easily punctured.
  2. The bag is 700 x 600mm. To protect the bag from the animals a guard made of chicken wire will be placed around it. The current system uses a circular guard of 500mm diameter, 1600mm circumference. The trial guards will require 2600mm of chicken wire, a 62% increase in wire. (higher cost).
  3. The height of the wick relative to the water level in the bag is critical because it determines drip frequency, too high above the water level causes the dripping to stop and too low and the dripping rate increases, emptying the bag too quickly. The wick is mounted in a support that can slide down a guide as the bag empties, maintaining the height relativity and the drip rate.
During 2013/2014, at the request of Dr. Cale, I conducted a 12 bag trial. The bags were placed around 12 Sand Hill Wattle, Acacia ligulata seedlings. This trial was successful. All 12 plants survive today, 5 years after planting. This first trial was different in many respects.
  1. Plant species was different
  2.  They were planted with their root system approx 300mm into the sand.
  3. The soil was sand, with no clay or binding material. Hence water could easily soak down into the sand, encouraging deeper root development.
  4. The weather was kind. For half the trial period there was occasional rainfall. 60mm falling in one day and 3 other 20mm rainfall events. I continued to refill the bags monthly.
  5.  There were only kangaroos in the site, no goats. Kangaroos like to eat Acacia Ligulata but the guards were fairly successful in keeping them away.
 
The 2018/2019 Trial.
 
The trial was to be of 50 bags, with 30 bags to be placed in a site in Rosies Dam area and 20 bags in an area in Site 12 (Stone Henge) of the original revegetation program. Murray Valley Pine, Callitris gracilis was chosen as the species to be planted.
The bags were placed in the two sites, filled with water and the guards placed around them by members of the Calperum and the Environment committee (CATE) on July 28th in preparation for planting.
During the following week, members from the Rotary Club of Coromandel Valley visited Calperum. They inspected the bags and refilled most of the bags because the wicks were too low. The wicks were reset.
During the next week, (August 7th and 8th) the 50 seedlings were planted and the bags topped up by members of the Rotary Club of Mitcham.
The bag refilling has been done by the Rotary Clubs of Onkaparinga, Berri, Flagstaff Hill and Adelaide during their visits to Calperum. The program will be evaluated after August 2019.
There has been a problem with the goat population at the Rosies Dam site. They have come into the area from the Mallee country in search of water.A number have been caught but more are present. The goats have damaged the guards and water bags and eaten 20 of the plants, in some cases to the ground level and the remainder leaving an approx 5 cm stem.5 seedlings are growing OK and the other 5 are stressed, which does not necessarily mean they will die but need watering.
The Stone Henge site is progressing much better. No goats have visited the site, resulting in 9 seedlings growing OK, 7 are stressed and 4 have died.
The trial will be evaluated in August, when the seedling survival rate, seedling growth and the number of man hours used in the refilling will be determined and compared with the standard system.
The refilling will continue after August but at a less frequent rate to encourage the seedlings to develop a deeper root system for greater dry conditions tolerance.
A further evaluation will occur in August 2020.
David  Gooley
Rotary Club of Mitcham